Shaped articles of cellulose acetate, e.g. fibers and films, have achieved widescale commercial acceptance.
Cellulose acetate wherein not less than 92 percent of the hydroxyl groups are acetylated and which contains an acetic acid content of about 60.6 to 62.5 percent is commonly referred to as cellulose triacetate or primary cellulose acetate. Cellulose acetate wherein the molecular structure is partially hydrolyzed until an average of 2 to 2.5 acetate groups remain per glucose unit is commonly referred to as secondary cellulose acetate and commonly contains a lesser acetic acid content of about 54 to 59 percent.
Solvent evaporation techniques (e.g. dry spinning) heretofore have been utilized when forming shaped articles of cellulose acetate. As is well known in the art, the solubilities of cellulose triacetate and secondary cellulose acetate differ greatly. Accordingly, methylene chloride is commonly utilized as the major solvent when spinning solutions of cellulose triacetate, and acetone is commonly utilized as the primary solvent when spinning solutions of secondary cellulose acetate. While methylene chloride will dissolve secondary cellulose acetate, it has not been used commercially with this material for historical and economic considerations. Solutions of secondary cellulose acetate in acetone (e.g. 95.5 percent by weight) and water (e.g. 4.5 percent by weight) commonly have been extruded into an evaporation zone (e.g. warm air) wherein the solvent is evaporated to leave a product of almost pure secondary cellulose acetate. Installation costs for such a dry spinning operation tend to be great. Spinning speeds tend to be limited by the residence time required to evolve the solvent, and the reduced strength of the spin line while large quantities of solvent are present. Considerable capital and operational expense is involved in solvent recovery from the evaporative atmosphere.
Certain fiber-forming processes have been proposed in the past wherein specific fibers other than cellulose acetate have been formed through the utilization of phase separation from designated solvent systems which may be accomplished by a pressure differential. See, for instance, the work reported by M. M. Zwick in Applied Polymer Symposia, No. 6, pages 109-149 (1967) Interscience Publishers.
It is an object of the present invention to provide an improved process for the production of secondary cellulose acetate filamentary material and film.
It is an object of the present invention to provide an improved process for the production of secondary cellulose acetate filamentary material and film which can be carried out at a rapid rate in a relatively small area.
It is an object of the present invention to provide an improved process for the production of secondary cellulose acetate filamentary material which may be more economically implemented than dry spinning processes commonly utilized in the prior art.
It is another object of the present invention to provide an improved process for the production of a secondary celluose acetate filamentary material which readily may be employed to form a multifilament tow of an unusually high filament count.
It is a further object of the present invention to provide an improved process for the production of secondary cellulose acetate filamentary material and film wherein the spinning solvent may be recovered as a concentrated vapor, thereby reducing solvent recovery and purification costs.
These and other objects, as well as the scope, nature, and utilization of the process will be apparent to those skilled in the art from the following description and appended claims.